Numerous technologies have been known and proposed for converting a variety of biomass into a useful fuel. For instance, food grade biomaterials such as sugar, starch, vegetable oil and animal fats can be converted into a fuel product but competes with food production resources. Efforts to utilize non-food crops such as cellulosic materials can be converted into a biofuel though achieving a cost-effective process has been elusive.
Currently, only a small percentage of biomass can be converted into a biofuel. For instance, a food product such as corn kernels can be converted into ethanol but the stalks, husks, and similar cellulosic materials are unable to be converted. The availability of vegetable oil and animal fat making biodiesel is also limited and to the extent food resources are turned into a fuel, the cost of the starting material increases putting pressure on food supplies and making the source material more expensive for biofuel production.
While technologies exist to convert starch, sugars, vegetable oils and animal fats into either an ethanol fuel or a biodiesel, there remains a need within the art to utilize majority biomaterials such as non-food cellulosic materials, and cellulosic and lignin scrap material from other industries such as forestry waste and to utilize rapidly growing biomaterials such as grasses that can be converted into a suitable transportation fuel.
On the other hand, coal is a “dead” and “aged” biomass with enormous quantity, and has undergone numerous studies which yielded distinct commercial processes directed to direct or indirect liquefaction of coal, in which both need costly hydrogen production. Much of the coal chemistry are poorly understood due in part to the complex molecular structure of various types of coal. Given that there is no recognized repeating monomer unit in coal, it has been difficult to obtain cost effective, high yield liquefaction protocols.
To eliminate costly hydrogen production, hydrolysis of coal with alkali was investigated previously with limited success. Only low yields of alkali-soluble products were reported. One of the exception, set forth in U.S. Pat. No. 4,728,418, entitled “Process For The Low-Temperature Depolymerization Coal Its Conversion A Hydrocarbon Oil” (University of Utah), and which is incorporated herein by reference, describes a three step process using the steps of a metal chloride catalyst with partial depolymerization followed by a base-catalyzed depolymerization in an alcohol solution of an alkali hydroxide which is then further processed with an additional catalyst to obtain a hydrocarbon oil as a final product. While such a process is useful for obtaining a depolymerized coal, the process involves multiple steps using multiple catalysts.
Coal shares a lot of similarities with biomass (FIG. 1, reproduced from data in C. Keeling, Tellus XXV, 2, 174-198, 1973, and which is incorporated herein by reference), but is much more difficult to convert than biomass. The chemistry to break down coal clusters would convert hard-to-convert biomass, i.e., lignin and cellulose, as well as easy ones (starch, sugar, vegetable oil, animal fat). Accordingly, there remains room for improvement and variation in the art of biomass conversion to a fuel product.